Composite metallic bodies and method of producing the same



OCt- 1956 I H. R. NACK ETAL 2,767,464

POSITE METALLIC BODIES AND METHOD OF PRODUCING THE SAME FIG-3 {iMwML L Mf' INVENTOR I HERMAN. R. NAGK fgHgRwfigAgRE i ATT6RNEYS United StatesPatentO COMPOSITE METALLIC BODIES AND METHOD OF PRODUCING THE SAMEHerman R. Nack, Troy, and John Whitacre, Dayton, Ohio, assignors to TheCommonwealth Engineering gglrnpany of Ohio, Dayton, Ohio, a corporationof Application October 24, 1952, Serial No. 316,695

Claims. (Cl. 29-194) This invention relates to composite metallic bodiesand to methods of producing the same. More particularly the inventionrelates to the coating of steel with chromium through the intermediaryof a nickel tie ply or bonding layer.

Chromium is a rust-defying metal, hard but relatively brittle;- in theplated condition whether attained by electrolytic or gas plating methodsit shows adherence to some degree for steels. This adherence however,probably due to the brittle characteristic is not entirely satisfactoryfor applications involving high stresses and temperatures such as mayoccur in gun barrels.

It is a particular object of this invention to describe a novel methodfor attaining improvement in the characteristics of chromium platedobjects.

It is an important object of this invention to describe a novelcomposite metal product of improved physical characteristics having awear surface of chromium.

These and other objects of the invention are attained by coating theobject to be plated with metal or metals deposited from the'vapor stateby the thermal decomposition of metal bearing compounds; in the presentinstance a thin adherent coating of nickel is first deposited on theobject to be plated and thereafter chromium is similarly deposited overthe nickel.

The product attained by the generally described method comprises abaselayer, a thin nickel layer preferably having a thickness of less thanone mil, and a heavy chromium layer. The chromium is thus supported onnickel which is considerably more ductile and malleable than thechromium. Accordingly under the application of stress the nickel willhave a-slight tendency to yield and take up the effects of the appliedforces relieving to a degree the strains in theupper more brittlechromium layer.

The thickness of the nickellayer may be important in connection withsome applications butis not to be consideredas critical; it shouldhowever be thin relative to the chromium and the onlylimitationis thatthe nickel underthe applied stresses should not flow to an extent thatpermanent deformation occurs. A layei of nickel which approaches themonomolecular. is considered to be satisfactory. t

The thickness of the chromium coat is preferably at least several-timesthatof the-nickel layer and the ratio may be as muchas. 10:1. Withgreater ratios the ability of the nickel to absorb stresses sufficientlyquickly will be impaired.

The process of invention is particularly adapted for the plating ofsteelobjects of substantially all qualities and characteristics and theinvention will accordingly be described withparticular referencethereto.However other materials capable of withstanding the temperature involvedmay be similarly treated and .the inventive concept is not to beconsidered as limited to steel and various iron alloys.

In the practice of the invention then the steel surface is first cleanedand activated as described hereinafter and is then brought to a suitabletemperature range capable of promoting the thermal decomposition of theselected nickel bearing gaseous compound.

Adherence of the nickel plate to the steel is promoted by maintainingthe initial deposition rate low. While high plating gas flow rates andhigh plating gas concentrations produce acceptable results it ispresently considered that adherence and uniformity of coating areimproved by first securing a microscopic coating over which additionalnickel deposition may suitably take place at a relatively fast rate.This microscopic or monomolecular coating is favorably attained asdescribed with particularity hereinafter when both the gas concentrationand plating gas flow rates are maintained relatively low.

The plating gas is to be understood as the metal bearing gas; theprocess is conducted with the aid of a carrier gas and While hydrogen ispreferred for such purpose due to its tendency towards a reducing actionothers such as nitrogen, carbon dioxide and carbon monoxide may besuitably employed in the practice of this invention.

Upon attainment of the required nickel coating the airtight platingchamber is preferably swept free of all gases, and to insure of acompletely free nickel surface the same may be subjected to heating toevolve all gases. Thereafter the gaseous chromium compound is introducedwith the aid of a carrier gas. Apparently adhesion will also befacilitated if the initial chromium plating is performed slowly theratebeing increased after an initial chromium layer has been deposited.

Alternatively Where desired the nickel coated body may be removed fromthe plating chamber before the chromium is applied, but if thisprocedure is followed thOl'Ollgr deoxidation with hydrogen or otherreducing agent should take place prior to chromium deposition.

The gaseous sources of the nickel and chromium are not critical to thisinvention; however nickel carbonyl and chromium hexacarbonyl arepreferred as the sources of nickel and chromium respectively.

The invention will be more fully understood by refer ence' to thefollowing detailed description and the accompanying drawing wherein:

Figure 1 is a sectional view of an object coated with chromium andnickel in accord with the precepts of this invention;

Figure 2 is a sectional view of a cylindrical workpiece coated inaccordance with this invention; and

Figure 3 is a view taken on line 3-3 of Figure 2.

As a specific example of the process of invention a steel workpiece isfirst heated in an atmosphere of hydrogen to a temperature of betweenabout 800900 F. for a period of a few minutes which temperature is wellabove the normal plating range of nickel carbonyl; then with hydrogenflowing over the workpiece the temperature thereof is reduced to about350-400 F. and nickel car.- bonyl is slowly bled into the apparatus, thestream of hydrogen now acting as a carrier. The total gas flow at thistime may be about cc./minute approximately onethird of the gaseousvolume being nickel carbonyl. The carbonyl upon contacting the heatedworkpiece decomposes to deposit nickel in a very thin coating over thesteel surface. In the dilute concentration set out above a flow forabout 10 to 15 minutes will deposit a sufiicient amount of nickel toserve as the intermediate bonding layer.

At the end of the above indicated, or similarly suitable period of timewhich may vary somewhat with the nickel thickness desired, the nickelcarbonyl How is halted and hydrogen is again fed through the systemwhile the temperature is raised to approximately 500-600 F. to insure ofcomplete removal of all nickel carbonyl and decomposition gases thereofThe workpiece temperature is then again reduced to 350-400 P. which isthe normal plating range for chromium hexacarbonyl.

With the hydrogen still flowing chromium carbonyl is vaporized andcarried slowly into the system; the concentration of the chromiumhexacarbonyl may be as low as 10-15% in the initial stages of chromiummetal deposition and this concentration may be increased to 40-50% byvolume as plating progresses. It is not essential that the concentrationbe so regulated but it appears that initial plating at low concentrationmay result in superior bonding without blistering.

The plating at higher concentrations may be continued for a sufiicientlength of time to acquire the necessary uniform coating a thickness of2-3 mils being obtainable generally in about 30 minutes.

The interior of steel surfaces may be plated with suitable apparatussuch as that described in co-pending application of Peter Pawlyk, SerialNo. 250,306, filed October 8, 1951, and assigned to the same assignee asthe present invention, although it is to be understood that theinvention is not to be limited thereto, since the process is clearlyequally' adapable to the production of coatings on the exterior surfacesof articles.

Referring to the drawing, Figure 1 shows a steel base 1 coated with avery thin layer which may be taken as substantially monomolecular, ofnickel having thereon a layer 3 of chromium. In the structure of Figures2 and 3 the steel base 5 in cylindrical form is provided with a nickellayer 7 over which is positioned the cylindrical layer 9 of chromiumdeposited from the vapor state.

It is to be noted that while other gases may be substituted for thehydrogen in its action as a carrier in the production of the productthat a reduction gas, e. g. hydro gen, is considered necessary to thepreliminary steps involving cleaning and de-oxidation of the steel orother similar surface.

The product thus produced will have, due to the noted ductility andmalleability of the nickel, superior service characteristics.

It will be understood that this invention is susceptible to modificationin order to adopt it to different usages and conditions and accordingly,it is desired to comprehend such modifications within this invention asmay fall within the scope of the appended claims.

We claim:

1. In a process of gas plating nickel upon steel the steps of heatingthe steel briefly in an atmosphere of hydrogen at between about 800-900E, cooling the steel into the plating range of nickel carbonyl,introducing nickel carbonyl to the steel to effect deposition of nickelthereon, and depositing onto the resultant nickel plated steel chromiummetal by subjecting the same to gaseous chromium carbonyl at atemperature to effect decomposition of the chromium thereon to athickness of from about 1 to 10 times that of said nickel.

2. In a process of gas plating nickel upon steel the steps of heatingthe steel briefly in an atmosphere of hydrogen at between about 800-900F., cooling the steel to between about 350-400 F., introducing nickelcarbonyl to the steel to eflect deposition of nickel thereon, andsubjecting said nickel plated steel to gaseous chromium carbonyl at atemperature to efiect decomposition of the chromium carbonyl anddeposition of the chromium thereon to a thickness of from about 1 to 10times that of said nickel.

3. In a process of producing a gase plated composite metal body thesteps of successively depositing on a metal base from heat decomposablegaseous metal bearing carbonyl compounds nickel and chromium, andheating the base in an atmosphere of a reducing gas to a temperaturewell in excess of normal plating temperatures prior to each metallicdeposition.

' 4. In a process of producing a gas plated composite metal body thesteps of successively depositing'on a metal base from heat decomposablegaseous metal bearing carbonyl compounds nickel and chromium, andheating the base in an atmosphere of hydrogen to a temperature well inexcess of normal plating temperatures prior to each metallic deposition.

5. In a process of producing a gas plated composite steel body the stepsof briefly heating the steel in an atmosphere of hydrogen at betweenabout 800-900 F., cooling the steel into the plating range of nickelcarbonyl, introducing the nickel carbonyl to the steel to deposit a thinsubstantially monomolecular film of nickel thereon, heating the steeland nickel composite to a temperature well above the normal platingrange of chromium hexacarbonyl in the presence of hydrogen, cooling tothe plating range of chromium hexacarbonyl, and introducing chromiumhexacarbonyl to the composite body to effect deposition of chromium of agreater thickness than said deposited nickel on said nickel, saidchromium deposit being on the order of between about 1 to 10 times thethickness of said nickel.

6. In a process of producing a gas plated composite steel body the stepsof briefly heating the steel in an atmosphere of hydrogen at betweenabout 800900 F., cooling the steel to between about 350-400 E,introducing nickel carbonyl to the steel to deposit a thin substantiallymonomolecular film of nickel thereon, heating the steel and nickelcomposite to a temperature well above the normal plating range ofchromium hexacarbonyl in the presence of hydrogen, cooling to theplating range of chromium hexacarbonyl, and introducing chromiumhexacarbonyl to the composite body to effect deposition of chromium onsaid nickel, said chromium deposit being on the order of between about 1.to 10 times the thickness of said nickel.

,7. In a process of producing a gas plated composite steel body thesteps of briefly heating the steel in an atmosphere of hydrogen atbetween about 800-900 F., cooling the steel to between about 350-400 F.,introducing nickel carbonyl to the steel to deposit a thin substantiallymonomolecular film of nickel thereon, heating the steel and nickelcomposite to between about 500-600 F. in the presence of hydrogen,cooling to between about 350-400 F., and introducing chromiumhexacarbonyl to the composite body to efiect deposition of chromium ofgreater than a monomolecular thickness on said nickel, said chromiumdeposit being on the order of between about 1 to 10 times the thicknessof said nickel.

8. In a process of gas plating, the step (a) heating a steel workpiece,the step (b) plating from a heat decomposable gaseous nickel bearingcompound a substantially monomolecular coating of nickel onto saidworkpiece, and the step of (c) plating from a heat decomposable gaseouschromium bearing compound a coating of chromium greater in thicknessthan said nickel upon said nickel, said chromium deposit being on theorder of between about 1 to 10 times the thickness of said nickel.

9. A composite metal body produced in accordance with the process ofclaim 3.

10. A composite metal body produced in accordance with the process ofclaim 4.

References Cited in the file of this patent UNITED STATES PATENTS1,578,254 Bennett Mar. 30, 1926 1,615,585 Humphries Ian. 25, 19272,475,601 Fink July 12, 1949 2,514,873 Keene et al July 11, 19502,516,058 Lander July 18, 1950 2,525,831 Scherer Oct. 17, 1950 2,612,442Goetzel et al Sept. 30, 1952

3. IN A PROCESS OF PRODUCING A GASE PLATED COMPOSITE METAL BODY THE STEPS OF SUCCESSIVELY DEPOSITING ON A METAL BASE FROM HEAT DECOMPOSABLE GASEOUS METAL BEARING CARBONYL COMPOUNDS NICKEL AND CHRONIUM, AND HEATING THE BASE IN AN ATMOSPHERE OF A REDUCING GAS TO A TEMPERATURE WELL IN EXCESS OF NORMAL PLATING TEMPERATURES PRIOR TO EACH METALLIC DEPOSITION.
 9. A COMPOSITE METAL BODY PRODUCED IN ACCORDANCE WITH THE PROCESS OF CLAIM
 3. 